Asymptomatic paroxysmal ventricular standstill in an elderly male following revascularization of multivessel coronary disease: A case report and literature review

Key Clinical Message Ventricular standstill is a dangerous arrhythmia that requires prompt diagnosis and intervention, especially in patients with structural heart disease. Clinicians should recognize ventricular standstill as a complication of cardiac revascularization and be cognizant of asymptomatic cases necessitating intervention. Early evaluation to facilitate pacemaker implantation portends good outcomes in this patient subgroup.


| INTRODUCTION
Ventricular standstill is an uncommon arrhythmia that typically manifests with cardiac arrest.Provoked by interruption of ventricular conduction, early diagnosis is challenging due to most cardiac arrests occurring outside of the hospital.This arrhythmia has been detected in a broad range of clinical scenarios including fulminant myocarditis and as a complication of repair of congenital heart disease.We present an atypical case of asymptomatic ventricular standstill that developed following coronary artery bypass grafting in an elderly male with multivessel coronary disease.

| HISTORY OF PRESENTATION
A 70-year-old male presented for elective coronary artery bypass grafting (CABG) after left heart catheterization showed triple vessel disease not amenable to percutaneous coronary intervention (PCI) and multiple in-stent restenosis (Video S1).In the 3 months prior to admission, he developed progressively worsening chest pain and exertional dyspnea, which prompted the ischemia evaluation.He underwent a nuclear stress test, which was positive for anterior and anterolateral reversible defects.His rest left ventricular ejection fraction (LVEF) was 47% and on stress there was a drop in his LVEF to 31% in addition to a significant drop in blood pressure from 125/77 to 106/44 mmHg.Limited echocardiogram demonstrated a mildly LVEF of 40%-45% and hypokinetic changes in the anterior and lateral walls (Video S2).On admission, he was afebrile to 36.7°C with a heart rate of 87 beats/min and a blood pressure of 130/84 mm Hg.His physical exam was largely unremarkable, including sinus rhythm without murmurs and clear lungs to auscultation.He was breathing comfortably on room air and did not have baseline supplementary oxygen requirements before admission.

| PAST MEDICAL HISTORY
This patient had a past medical history of obstructive coronary disease with multiple stents, hypertension, and Type 2 diabetes mellitus.He did not have any cardiac surgeries or arrhythmia diagnoses prior to this admission.At baseline, he was able to walk at a steady pace without developing cardiac and respiratory symptoms.He had a metabolic equivalent score (METS) of four and was in stable cardiovascular health since his last angiogram.

| INVESTIGATIONS
The initial electrocardiogram (EKG) showed sinus rhythm with frequent premature ventricular contractions and an atypical left bundle branch block (Figure 1).Cardiothoracic surgery performed a triple vessel CABG to left anterior descending (LAD), first branch of obtuse marginal (OM1), and first right posterolateral artery (RPL1) in addition to endarterectomy of the middle RPL1.The left internal mammary artery and saphenous vein were used to construct the grafts.For the entirety of the procedure, the patient was maintained on cardiopulmonary bypass and cooled to 34°C with cardioplegia administered every 15-20 min.Cardioplegia served to reduce myocardial oxygen demand in order to minimize the effects of ischemia during the surgery.Due to his obesity, the decision was made to perform sternal plating rather than wire cerclage for sternal reapproximation.Plate fixation is preferred in patients with advanced age and multiple comorbidities since they are at greater risk of developing sternal nonunion and infection postoperatively compared to wire cerclage. 1There were no immediate complications from the surgery, and the patient was transferred to the cardiac intensive care unit with temporary epicardial pacing wires.He briefly required hemodynamic support with peripheral norepinephrine, which was quickly tapered off.Routine chest tube that was placed perioperatively to drain excess mediastinal blood was removed the day after surgery.On postoperative day 1, a rhythm strip recorded 4 s of high-grade atrioventricular block with ventricular standstill (VS) (Figure 2).The patient remained asymptomatic during the event, including being fully alert and oriented without prodrome of presyncope or syncope.Unfortunately, telemetry continued to record multiple episodes of VS leading into postoperative day 2, all of which ranged from 3 to 5 s.During these events, he did not have syncopal symptoms, nor was he ever paced by his pacer wires.Analysis of electrolytes showed potassium ranged from 3.6-4.1 mEq/L, sodium 134-140 mEq/L, serum calcium 7.8-8.4mg/dL, and magnesium 2.1-2.5 mg/ dL.On postoperative day 3, the rhythm strip recorded atrial flutter with loss of capture with loss of capture from the epicardial pacer (Figure S1).Once again, he remained asymptomatic and did not require pacing from his pacer wires.ventricular tachycardia are often seen, but usually transient and do not require procedural intervention.Conduction disturbances and bradyarrhythmias such as atrioventricular node block and sinus node dysfunction are the least common types of arrhythmias observed post-CABG.

| MANAGEMENT
Due to the patient's dependence on his temporary pacemaker in the setting of multiple documented episodes of ventricular standstill, electrophysiology was consulted for placement of a permanent pacemaker.On postoperative day 5, a dual-chamber Boston Scientific pacemaker was successfully implanted without complications and a follow-up EKG recorded a paced rhythm without any runs of VS (Figure 3).His electrolytes, specifically potassium and magnesium, were analyzed daily, and his rhythm was monitored on telemetry until discharge.He did not require electrolyte repletion, and telemetry did not detect any concerning atrial or ventricular arrhythmias postoperatively.Basal-bolus insulin was administered to maintain his sugars between 140 and 180 as per hospital protocol.Arrangements were made for him to participate in cardiac rehabilitation therapy 1 month after discharge.

| FOLLOW-UP
The patient followed up in electrophysiology clinic where interrogation of his pacemaker did not reveal significant atrial nor ventricular events, no periods of undersensing, nor inappropriate pacing.An atrial and ventricular paced rate of less than 1% was recorded.He denied angina, cardiac palpitations, and syncopal episodes since his discharge.

| DISCUSSION
Ventricular standstill is an uncommon arrhythmia that occurs when conduction through the ventricles is interrupted, while the sinoatrial node remains functional. 2 For this reason, EKG displays p waves without succeeding QRS waves, as ventricular depolarization is inhibited.
Prevalence and incidence remain unclear, and many cases are likely missed as out-of-hospital incidents are likely to result in sudden cardiac death (SCD) if the patient is not being paced.Rubin et al. evaluated incidence of ventricular arrhythmias after CABG and found 57% developed complex ventricular arrhythmias including large premature ventricular contraction (PVC) burden, ventricular tachycardia, and R on T phenomenon. 3No perioperative risk factors were identified that predisposed the subjects to the arrhythmias, all of whom had normal LVEF.
This case highlights a unique presentation of VS as the patient remained completely asymptomatic despite never being paced by his pacer wires.This arrhythmia is known to be ten times more dangerous than ventricular fibrillation, making rapid diagnosis and intervention crucial to prevent hemodynamic collapse and SCD. 4 Underlying coronary artery disease (CAD) is evident in approximately 80% of SCD cases; however, 24-h ambulatory electrocardiography is preferred for optimal risk stratification. 5Although non-sustained ventricular arrhythmias can often be conservatively managed with continued telemetry monitoring and correction of underlying electrolyte deficiencies, affected patients with structural heart disease require stricter surveillance.Specifically, severe derangements in potassium and magnesium are established independent risk factors for lethal ventricular arrhythmias.Potassium has a role in maintaining myocardial electrical stability via the sodium-potassium adenosine triphosphatase pump. 6Adrenergic stimulation of this pump during myocardial ischemia can deplete potassium levels and predispose patients to ventricular arrhythmias and SCD. 6Magnesium regulates the activity of the renal outer medullary potassium (ROMK) channel and is inversely proportional to the open ROMK channel pores. 7Hence, decreased intracellular magnesium levels cause more ROMK channels to open and lead to potassium wasting and the development of lethal arrhythmias. 7espite the nonsustained paroxysmal pattern of VS in our patient, the fact that his arrhythmia repeatedly occurred while being continuously paced necessitated permanent pacemaker implantation.
To the best of our knowledge, asymptomatic VS following CABG has not been reported based on a comprehensive literature query of PubMed and Google Scholar.The majority of cases involved infectious etiology or profound vagal tone leading to bradyarrhythmia and eventually VS.Our literature review of published case reports in PubMed since 2000 identified 35 patients who developed VS (Table 1).Females accounted for 57% of cases and underlying structural heart disease was present in only 29% of patients.Myocarditis and excessive vagal tone were the two most common causes with each responsible for 20% of cases.Remarkably, only two patients (8%) were asymptomatic at the time VS was diagnosed during their hospital stay.Nine patients were excluded from this measurement due to being sedated on venoarterial extracorporeal membrane oxygenation (VA-ECMO), mechanically ventilated, or symptoms were not documented in the manuscript.We postulate many cases of VS go unreported as more than seventy percent of cardiac arrests and subsequent SCDs precipitated by this ventricular arrhythmia occur outside of the hospital. 8

| CONCLUSIONS
Ventricular standstill is a dangerous arrhythmia that requires prompt diagnosis and intervention, especially in patients with structural heart disease who are already at heightened risk for adverse cardiac events.Clinicians should recognize VS as a potential complication of cardiac revascularization and be cognizant of asymptomatic cases necessitating intervention.Early evaluation by electrophysiology to facilitate pacemaker implantation portends good outcomes in this patient subgroup.
Development of arrhythmias after CABG are a common occurrence and primarily include atrial fibrillation and atrial flutter.Ventricular tachyarrhythmias such as non-sustained F I G U R E 1 Admission electrocardiogram showing normal sinus rhythm with multiple premature ventricular contractions in anterior leads.An atypical left bundle branch block is visible in V1-V3.F I G U R E 2 Postoperative day 1 rhythm strip showing a 3-4 s run of nonsustained ventricular standstill in lead II.Pacer spikes from epicardial pacer wires are noted followed by a premature pacer spike, indicating undersensing of the pacemaker (red arrow).
Characteristics of patients and etiologies of ventricular standstill based on a query of PubMed case reports since 2000.
3 Postoperative day 5 EKG after implantation of dual chamber pacemaker.Patient is being ventricularly paced, although pacer spikes are not well visualized in this view.T A B L E 1 T A B L E 1 (Continued)